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904

Appendix IL

To avoid the evils of varying boiler pressure, a reducing valve
is now often used between boiler and cylinder, giving a lower
pressure, but steadiness and dryness, Reid's valve, Fig. 864, is a

good example. The steam entering at A, finds valve B closed by
spring c, so passes along E, and lifting the throttle valve F, acts
on the piston D and overcomes the compression of spring c, thus
allowing a free flow through D to G at a lower pressure. Now
the coiled pipe L is connected to vessel M, which is always full of
condensation water, and the low pressure acting on diaphragm N
tends to lift lever i and close valve r, thus throttling the pressure
on D to the right amount. The lifting tendency is also resisted
by the spring H, which can be screwed up against a scale K to give
and shew the required reduction.

When the hot-well water is returned to boiler, there is danger
due to the deposition of cylinder oils on the furnace crowns,
causing possible overheating. Feed-water Filters have been there-
fore introduced, of which Rankine's, Fig, 865, is an example.